Energy generation systems adaptable for burning dust-type fuels

ABSTRACT

An energy generation system, especially applicable to firetube boilers but also applicable to other combustion-type energy generators, for burning dust-type fuels such as wood sander-dust. The system comprises fuel metering apparatus, responsive to system demands, for accurately controlling the fuel-air ratio and modulating the mass flow rate of the dust-type fuel into the combustion chamber. Dust fuel, normally of variable density, is fed from a large storage hopper into a metering bin sized to hold only a small volume of the fuel. A rotary agitator within the bin equalizes the density of the dust fuel and divides it into equal volumetric portions which are passed in succession over an opening in the bottom of the bin. The size of the opening is variably modulated by a reciprocating metering gate whose position is determined by a controller responsive to system energy demands. Small predetermined quantities of the fuel, dependent upon the size of the opening, drop through the opening periodically and are transformed into a continuous homogeneous stream of dust fuel by a screw conveyor located below the opening. The conveyor feeds the stream of dust into a blower which transports the dust suspended in an air stream to a dust fuel burner. In the embodiment of the invention adaptable to firetube boilers, the burner comprises a modified boiler diffuser having one or more dust inlet tubes and a continuous supporting pilot to insure continuity of burning. The boiler embodiment also includes a boiler extension section having a trap for retaining any large particles of the fuel within the boiler to insure their complete combustion.

United States Patent Turner et al.

Sept. 2, 1197s ENERGY GENERATION SYSTEMS 1 ADAPIABLE FOR BURNING DUST-TYPE FUELS [75] Inventors: Leslie C. Turner; Harry Cockreham,

both of Lake Oswego, Oreg.

[73] Assignee: Turco Engineering, Inc., Lake Oswego, Oreg.

22 Filed: June 17, 1974 [21 Appl. No.1 479,622

Related U.S. Application Data [62] Division of Ser. No. 357,503, May 4, 1973, Pat. No.

[52] U.S. Cl 110/103; 110/101 C; 214/17 CA [51] Int. Cl. F23K 3/00 [58] Field of Search 110/10] R, 101 C, 102, 110/103, 104; 302/52, 56; 222/228; 214/17 R, 17 CA [56] References Cited UNITED STATES PATENTS 292,237 1/1884 Leede 302/56 X 542,477 7/1895 Jenkins... 302/56 X 993,929 5/1911 Welton 110/103 1,386,009 8/1921 McDonald. 302/56 X 2,228,751 l/194l Bros 110/102 2,912,943 11/1959 Nicolai et al. 110/104 Primary Examiner-l enneth W. Sprague Attorney, Agent, or Firm-Chemoff & Vilhauer [57] ABSTRACT An energy generation system, especially applicable to firetube boilers but also applicable to other combustion-type energy generators, for burning dust-type fuels such as wood sander-dust. The system comprises fuel metering apparatus, responsive to system demands, for accurately controlling the fuel-air ratio and modulating the mass flow rate of the dust-type fuel into the combustion chamber. Dust fuel, normally of variable density, is fed from a large storage hopper into a metering bin sized to hold only a small volume of the fuel. A rotary agitator within the bin equalizes the density of the dust fuel and divides it into equal volumetric portions which are passed in succession over an opening in the bottom of the bin. The size of the opening is variably modulated by a reciprocating metering gate whose position is determined by a controller responsive to system energy demands. Small predetermined quantities of the fuel, dependent upon the size of the opening, drop through the opening periodically and are transformed into a continuous homogeneous stream of dust fuel by a screw conveyor located below the opening. The conveyor feeds the stream of dust into a blower which transports the dust suspended in an air stream to a dust fuel burner. In the embodiment of the invention adaptable to firetube boilers, the burner comprises a modified boiler diffuser having one or more dust inlet tubes and a contin' uous supporting pilot to insure continuity of burning. The boiler embodiment also includes a boiler extension section having a trap for retaining any large particles of the fuel within the boiler to insure their com plete combustion.

9 Claims, 6 Drawing Figures r45 24 g i J41 [z- Ba I.

so so 2 I 4: l sa R 1 I 1s 74 7a. J \t 7e ENERGY GENERATION SYSTEMS ADAPTABLE FOR BURNING DUST-TYPE FUELS This application is a divisional of my co-pending application Ser. No. 357,503, filed May 4, 1973, now U.S. Pat. No. 3,825,937.

BACKGROUND OF THE INVENTION This invention relates to a combustion-type energy generation system, especially applicable to firetube boilers but also adaptable for use with other combustion-type energy generators, for utilizing dust-type materials as the primary fuel. More particularly, the system comprises demand-responsive metering apparatus capable of controlling the fuel-air ratio and mass flow rateof the dust fuel with a degree of accuracy comparable to that obtainable with gas and oil fuels.

In the past, wood dust waste produced by lumber sanders (hereinafter referred to as sanderdust) has been utilized as a fuel supplement in watertube boilers and other large heating devices. However considerable difficulty has been encountered in attempting to employ the sanderdust as the major component of the total fuel supply. One of the difficulties referred to is that the burning of sanderdust as a primary fuel tends to cause extremely high temperatures within the combustion chamber, resulting in accelerated deterioration of the combustion chamber walls. In addition, with sanderdust as the major component of the fuel supply, continuous accurate metering of the fuel mass flow rate into the combustion chamber in accordance with the desired air-fuel ratio and energy demands of the system is virtually impossible, thereby causing further problems. For example the mass flow rate of fuel to a boiler must be responsive to boiler pressure, so as to increase the fuel supply in response to lower boiler pressure and decrease the supply in response to higher pressure relative to a predetermined pressure setting. If the fuel mass flow rate is not accurately responsive to boiler pressure, pulsing of the boiler due to uncontrolled fluctuations in energy input, and possible explosion, may result. In addition, the lack of adequate control of the fuel-air ratio may cause incomplete fuel combustion and thus excessive pollutants in the flue gases, re-

sulting in violation of applicable governmental regula tions concerning flue gas purity.

As a consequence of these various difficulties it has been necessary, in prior art systems utilizing sanderdust as a fuel component, to employ a more easily metered fuel such as natural gas or oil as the major component of the fuel supply, employing the sanderdust only as a fuel supplement to limit the foregoing deterimental effects of the dust-type fuel. This practice is expensive however, requiring substantial amounts of purchased fuel and high-capacity equipment, such as watertube boilers, to utilize and disposeof sufficient quantities of the sanderdust waste. Consequently most small producers, who do not have sufficient energy requirements to warrant the cost of high-capacity energy generators, continue to be faced with sanderdust waste disposal problems while at the same time having to resort primarily to purchased gas or oil fuels to satisfy their en ergy requirements.

The metering problems connected with the use of sanderdust referred to above, which have prevented its use as a primary fuel, are caused principally by the nonuniform density characterizing such fuel. As evidenced by the systems shown in Bros U.S. Pat. No. 2,228,751 and Daniels U.S. Pat. No. 2,621,083, attempts have been made to meter the flow of dust-type fuels into a combustion chamber by controlling the speed of a screw conveyor which transports the fuel. However, since the density of the compacted dust transported by each turn of the conveyor may vary widely, thereby uncontrollably varying the mass flow rateof the injected fuel, such systems do not eliminate the foregoing problems. Accordingly a need presently exists for apparatus, adaptable to boilers and other types of energy generation systems, capable of continuously and accurately controlling the fuel-air ratio and metering the mass flow rate of dust-type fuels in response to system energy demand, so as to permit such systems to utilize dust'type materials as the primary fuel source without causing unacceptable pollution of the flue gases or uncontrolled energy pulsing. In addition, such system should be of the type capable of limiting combustion chamber temperatures so as to avoid accelerated deterioration of the chamber walls.

SUMMARY OF THE PRESENT INVENTION The present invention is directed to an energy generation and combustion system capable of utilizing a dust-type fuel, particularly sanderdust, as its primary fuel (constituting up to of the total fuel energy input) while eliminating all of the abovementioned prob lems normally encountered with dust fuels.

The fuel supply portion of the system includes a metering bin for accepting dust fuel of variable density from a large storage hopper, the metering bin being sized to hold only a small volume of the fuel so as to minimize any tendency of the fuel to become compacted in the bin. Fuel level sensors are provided for selectively starting and stopping a conveyor which transports the fuel from the storage hopper into the metering bin, and a further sensor is provided for interrupting the supply of dust fuel to the burner if the fuel in the metering bin drops below a predetermined level. A rotary agitator, comprising equally spaced radial paddles, loosens and homogenizes the dust fuel in the bin, equalizing its density and dividing it into equal mass portions which are passed in succession over a discharge opening in the bottom of the bin. A reciproeating metering gate, movable by means of a controller responsive to system energy demands, determines the size of the discharge opening and thereby determines the mass of small increments of the fuel which periodically drop through the opening as the agitator rotates. The agitator and discharge opening cooperate to prevent any compaction of the fuel during the metering step to maintain the homogeneity established within the metering bin and thereby maintain a consistent predetermined rnass flow rate variable only in response to movement of the metering gate. A screw conveyor located below the opening, having a volumetric capacity substantially greater than that needed to transport the fuel so as to further guard against any densification or agglomeration of the fuel, transforms the increments into a continuous homogeneous stream of loose dust fuel and feeds the stream into a blower-powered pneumatic conveyor which mixes the dust with a supporting air stream and transports it through a dust inlet conduit into the combustion chamber.

In its preferred form, the system utilizes sanderdust as the major fuel component for a firetube boiler which, because'of its water-jacketed combustion chamber, is particularly adaptable for rapidly dissipating heat from the combustion chamber'and thereby effectively preventing accelerated deterioration of the chamber walls due to the high temperatures characterizing dust burning. The boiler is preferably modified by the provision of an extension section at one end thereof, havinga trap for retaining'within the boiler any gross particles contained in'the fuel so as to insure their complete combustion and prevent their escape with the flue gases. The diffuser section of the boiler is also modified by the inclusion of one or more dust inlet conduits anda gas or oil supporting pilot to insure continuity of burning.

The provision of a metering bin for transforming dust "fuel of variable density into a homogeneous mixture of uniform density, coupled with the metering agitator and gate for discharging periodic fuel increments from the bin in quantities of predetermined mass and the screw conveyor for transforming the increments into a continuous homogeneous stream, all without increased densification of the fuel, cooperate to insure that the dust fuel will enter the combustion chamber at a con stant predetermined mass flow rate variable only in response to variations in the adjustment of the gate. Thus the fuel-air ratio can be continuously and reliably controlled. In addition, the variable metering gate continuously insures that the fuel'flow rate is proportional to system energy demands. Accordingly the pulsing and pollution problems encountered previously when dust.

fuelswere used as the primary fuel component are eliminated. The provision of a continuous supporting pilot flame enhances the foregoing advantages by insuring smooth'and continuous burning of the fuel, while the provision of a trap in the combustion chamber for collecting and retaining unusually large particles in the fuel'stream further insures against the presence of unacceptable pollutants in the flue gases.

Accordingly it is a primary objective of the present to provide an energy generation system, adaptable for utilizing dust-type fuel as the primary fuel component, having fuel metering apparatus for continuously insuring a predetermined mass flow rate of such fuel into the combustion chamber variable only in response to control parameters such as system demands, thereby eliminating the possibility of uncontrolled energy pulsing or unacceptable pollutant content in the flue gases.

It is a further objective of the present invention to adapt a firetube boiler to burn dust-type fuel, especially sanderdust, as a primary fuel so as to take advantage of the special heat dissipation features of such boiler to alleviate the excessive temperature problems normally occasioned by dust fuel burning.

The foregoing and other objectives, features and advantages of the present invention will be more readily understood upon consideration of the following detailed description of the invention taken in conjunction with the accompanying drawings.

1 BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partially schematic assembly view of an energy generation system adapted for burning dusttype fuels depicting an enlarged, partially sectional side view of the fuel'metering pin and its associated equipment. I FIG. 2 is a top view of the agitator employed in the metering bin.

- FIG. 3 is a perspective detail view of the discharge opening and movable gate adjacent the bottom of the metering bin.

FIG. 4 is a perspective view of a boiler burner and diffuser assembly modified to accommodate dust fuel injection.

FIG. 5 is a side view of a multi-pass firetube boiler modified by the addition of a boiler extension section in accordance with the present invention.

FIG. 6 is a sectional view of the boiler extension section taken along lines 6'-6 of FIG. 5.

DESCRIPTION OF THE PREFERRED EMBODIMENT With reference to FIG. 1, the energygeneration system of the present invention comprises an energy generator 10, preferably a firetube boiler modified'in a manner to be described hereafter, and dust fuel'feed apparatus designated generally as 12 for supplying metered dust fuel to the combustion chamber of the boiler 10. The dust fuel preferably constitutes sanderdust waste produced by power sanders of the type which treat plywood, hardboard and other lumber products, such dust being substantially dry (approximately 6-15% moisture content by weight) and having an average particle size of approximately ten microns. A small quantity of gross wood particles, such as shavings or splinters, of a size much larger than the dust particles, is usually found mixed with any given quantity of sanderdust. Such waste presently represents a major disposal problem for the woodproducts industry but has the potential, if used as a fuel, to decrease substantially the cost of purchased fuels required for energy generation.

The dust fuel may be stored in a large storage hopper of any convenient design (not shown), from which it is emptied gradually through a conduit 14 in response to the rotation of a large feed screw conveyor 16 rotatably powered by a motor 18. The screw conveyor 16 empties the dust fuel through a chute 20 into a metering bin 22 having a volumetric capacity much smaller than that of the fuel storage hopper. The bin 22 is equipped with a pressure relief door 23 adaptable to be easily dislodged in response to any pressure-build-up in the bin 22, so as to guard against any possibility of explosion within the bin. Protruding through the wall of the bin 22 at different predetermined heights are a pair of level sensors 24, 26 respectively, each preferably of the type having a rotor member 28, 30 inside the bin rotatably driven by an electric motor whenever such rotation is not impeded by surrounding dust fuel and, whenever such rotation is impeded, causing a reverse torque which actuates a level sensing switch. The two level sensors are coupled by electrical circuits 32, 34 to the screw conveyor motor 18 in such a way as to selectively control the input of current to the motor through a power line 36. Whenever the level of the dust fuel in the bin 22 is high enough to impede the rotation of the rotor 28, the switching device in the level sensor 24 interrupts power to the motor 18 and stops the conveyor 16 from depositing fuel into the bin 22. The conveyor remains stopped until the fuel in the bin drops below the levelof the rotor 30, thereby permitting the rotor to turn. This in turn causes a signal to be transmitted by the switching mechanism of level sensor 26 closing the power circuit of motor 18 and restarting the conveyor 16 to deposit additional dust fuel into the bin.

The conveyor 16 continues operating until the fuel level once more reaches the rotor 28, at which time the switching mechanism of the level sensor 24 interrupts power to the motor 18, and so forth.

The dust fuel entering the metering bin 22 through chute 20 will normally'be of variable density due to its long period of repose in the storage hopper and the mechanical compressiveforces exerted on it'by the screw conveyor 16. The purpose of the metering bin 22 is to homogenize the dust fuel and equalize its density so that its mass flow rate into the combustion chamber of the boiler can be regulated accurately. To this end the size of bin 22 and the spacing of the level sensors 24, 26 are such that the amount of fuel added by each start of conveyor 16 is only enough to accommodate the boiler 10 for approximately minutes. This small capacity of the bin 22 causes a relatively rapid turnover of fuel in the bin, thereby insuring that it Will not have much chance to settle and become compacted by virtue of its own weight. In addition, the level sensor ar rangement insures that the height of the material in the bin, and thus its compressive weight, will be subject to little variation during operation.

Aided by the foregoing features, a rotary agitator 38 is provided within the bin to homogenize and equalize the density of the fuel dust. The agitator comprises eight paddle members 40 (FIG. 2), secured together by reinforcing bars 41, equally spaced radially about a vertical drive shaft 42 powdered by a motor 44 through a chain and sprocket assembly 46. The paddles 40 are driven by the shaft 42 at a constant speed of approximately 20 rpm to provide the necessary agitation. Con currently a plow member 48, also driven by the shaft 42, insures that the height of the fuel dust across the bin will be level rather than being permitted to pile up on the side where the fuel enters through the chute 20, thereby equalizing gravitational pressure on the fuel throughout the bin and promoting uniform fuel density.

The homogeneity of the fuel dust is greatest at the bottom of the bin where the fuel is divided into eight equal segments between adjacent pairs of paddles 40. As the paddles rotate, an increment of each successive fuel segment falls through a rectangular discharge opening 50 (FIGS. 1 and 3) formed in the bottom 51 of the bin 22 below the area of rotation of the paddles. Since the paddles rotate at constant speed, and since the density of the successive fuel segments is uniform, the mass of each such fuel increment is predetermined by the size of the discharge opening 50. As long as the area of the opening remains constant, the mass flow rate of the increments passing through the opening also remains constant. Conversely, any variation in the size of the opening causes a corresponding variation in the mass flow rate of the fuel.

As shown most clearly in FIG. 3, a reciprocating metering gate 52 having a rectangular opening 54 formed therein is provided for varying the effective size of the discharge opening 50. The position of the gate 52 is re sponsive to an electrically operated controller 56 of any suitable type, such as a Honeywell modutrol unit, which controls the reciprocation of the gate 52 through a linkage assembly 58. The controller 56, in turn, is responsive to signals received .through line 60 from a standard energy demand sensing device 62, such as a Honeywell pressuretrol, which regulates both the amount of fuel and the amount of air admitted to the combustion chamber of the boiler 10. Fuel regulation is accomplished through controller 56, Whereas air flow is modulated by means of a conventional damper within the boiler controlled by a reciprocating arm 64 acting on a damper lever 66. In this way the device 62 regulates both the air-fuel ratio and the absolute mass flow rate of both the fuel and the air in response to variations in energy demands of the system. In the boiler embodiment, the energy requirements are sensed as a function of the boiler steam pressure, and accordingly if boiler pressure drops below a predetermined level the demand response device 62 operates to increase both the air and fuel flow rates. Conversely, if boiler pressure increases to a level higher than a predeter mined limit, the device 62 reduces both the fuel and air input.

The accuracy ofthe foregoing control over the fuelair ratio and absolute fuel flow rate depends on the capability of the fuel metering apparatus to deliver a consistent, predetermined mass flow rate of fuel in response to a particular signal received from the device 62. If the density of the dust fuel being metered were not uniform, the fuel increments passing through the discharge opening 50 at any particular setting of the metering gate 52 might be volumetrically equal but not necessarily equal with respect to mass, thereby causing uncontrolled fluctuations in fuel-air ratio and in the fuel energy input tothe combustion chamber. Such is the problem encountered with prior art screw conveyor metering apparatus, which causes variable compaction of the fuel while transporting it through the screw and thereby causes uncontrolled variations in mass flow rate despite precise control of the screw speed. Accordingly the metering apparatus of the present invention, specifically the metering agitator 38 and discharge opening 50, cooperate to homogenize the fuel equalize its density prior to metering and then, during metering, prevent the fuel from being compacted to a density greater than that to which it has been previously homogenized by permitting the fuel simply to fall by gravity in periodic increments through an opening of predetermined size. This insures a consistent mass flow rate of the fuel from the bin, variable only in response to adjustment of the metering gate 52.

The periodic fuel increments passing through the discharge opening 50, while having a reliable mass flow rate, are not yet in continuous stream form suitable for introduction into the boiler combustion chamber. Accordingly a screw conveyor 68 driven by a motor 70 is included as part of the metering apparatus to receive the increments from the discharge opening 50 and transform them into a continuous stream. It is important that the screw conveyor 68 have a volumetric capacity substantially in excess of that necessary merely to transport the fuel increments received, so that the conveyor will not cause compaction of the dust fuel which would otherwise tend to destroy the uniformity of the mass flow rate. Accordingly the conveyor 68 is preferably of such a capacity and operates at sufficient speed that the fuel can be carried along therein at a level at or below the longitudinal axis of the conveyor, as indicated by the fuel level line 72 shown in phantom in FIG. 1. With such high volumetric capacity relative to the fuel flow, the screw conveyor 68 has no opportunity to compact the fuel dust but rather merelytransforms it into a continuous, evenly flowing stream.

The fuel stream is fed from the screw conveyor 68 through a conduit 74 into the intake of a pneumatic conveyor blower 75 powered by a motor 76. The blower 75 mixes the fuel with air entering through an inlet 78 and transports the fuel by means of the supporting air stream through a fuel feed inlet conduit 80,

at a linear speed greater than the possible speed of flame propagation back through such conduit, to a modified burner and diffuser assembly 82 mounted within the combustion chamber of the boiler 10.

As best seen in FIG. 4 the burner and diffuser assembly 82, as originally provided by the boiler manufacturer, comprises a conventional rotary damper 84 operated by the aforementioned lever 66 for controlling the influx of air from the boiler blower 86 into the combustion chamber. Also included are a set of airstraightening vanes 90 and a diffuser 92 having directional apertures 94 formed in the face 95 thereof for directing the combustion air into a swirling pattern as it is emitted from the face of the diffuser. The assembly 82 also normally includes a natural gas starting pilot 96 and, assuming that the boiler is intended to be operated selectively either on gas or oil fuel, an oil gun is provided in the opening 98 in the center of the diffuser 92 with gas jets surrounding the perimeter of the diffuser (not shown).

In the present invention, where the objective is to burn primarily dust-type fuel rather than primarily gas or oil fuel, certain modifications to the burner and diffuser assembly 82 are required. One of these is the addition of at least one dust fuel inlet conduit 80 protruding through the face of the diffuser 92, such conduit preferably having a directional end piece 100 facing tangentially to the swirl pattern of the diffuser so as to introduce the dust fuel smoothly and evenly into the combustion air emitted from the face of the diffuser. Depending upon the size of the boiler, one or more such dust inlet conduits 80 spaced around the diffuser may be desirable. In addition, a gas or oil supporting pilot 102 is mounted in the face of the diffuser, such supporting pilot having a fuel control valve 104 responsive to the boiler master control 106 (see FIG. 1) for supplying fuel to the pilot 102 continuously concurrently with the injection of the dust so as to insure continuous combustion of the dust fuel. The quantity of gas or oil fuel supplied to the supporting pilot 102 preferably constitutes about ten percent of the total fuel energy input to the combustion chamber of the boiler, the remainder of the fuel energy input being derived from the dust fuel. In the embodiment of the modified burner and diffuser assembly 82 shown in FIG. 4, the supporting pilot 102 is depicted as occupying the opening 98 in the center of the diffuser 92 where the oil gun provided by the boiler manufacturer is normally located. Alternatively, one or more such supporting pilots, depending upon the size of the boiler, may be mounted in the face 95 of the diffuser. A photoelectric scanner 108, provided by the boiler manufacturer for sensing the presence of a combustion flame at the face of the diffuser, operates through the master control 106 to selectively interrupt the introduction of fuel into the combustion chamber in response to any interruption in the combustion flame, in a mamner to be described more fully hereafter.

With reference'to FIG. 5, the boiler is preferably of the firetube type, so as to take advantage of its water-jacketed combustion chamber construction and resultant high heat dissipation characteristics which are desirable when utilizing a dust-type fuel as the primary fuel source. The primary combustion chamber comprises a long tube 88 extending substantially the length of the boiler 10, surrounded completely by water for generating steam. Although any type of firetube boiler may be adapted for utilizing dust-type material as the primary fuel, the preferred type is a multi-pass boiler wherein the combustion gases, after being emitted from the chamber 88, are directed again through the boiler in a series of successive passes through tubes 110, 112 and 114 respectively until the gases are finally vented to the atmosphere through stack 116.

A potential problem with the use of dust-type fuel, particularly sanderdust waste, is that occasional gross particles such as shavings and splinters much larger than the average dust particles are contained in the fuel. Although the combustion system heretofore described is capable of effecting complete combustion of the normal dust particles, such gross particles will not be completely burned if they are simply permitted to flow through the boiler pursuant to the normal combustion gas flow pattern. Accordingly the boiler 10 is preferably modified by providing a trap in communication with the combustjion chamber 88 for catching and retaining such gross particles within the boiler, thereby insuring their complete combustion and preventing the presence of unacceptable amounts of combustible pollutants in the flue gases. Such trap preferably is included in a boiler extension section 1 18 adaptable to be inserted on the end of the boiler opposite the dust burner and diffuser assembly 82 between the boiler body and the boiler door 120. As best seen in FIG. 6, the boiler extension section 118 is lined with a suitable refractory material 122 and contains a open trap 124 at its bottom into which the gross combustibles may fall by force of gravity after their exit from the combustion chamber 88 and prior to their entry into the multi-pass tube network. Periodically, the accumulation of ashes in the trap 24 may be removed from the trap 124 through removable doors 126, 128. For a multi-pass boiler of the type shown in FIG. 5, the boiler extension section must include a baffle such as 130, corresponding to the baffle 132 in the boiler door 120, for preserving the original flow pattern of the combustion gases through the boiler.

Operation of the energy generation system is initiated by the actuation of a switch 134 provided on the master control box 106. This starts a conventional timing sequence built into the master control whereby the blower 86 is first actuated for a predetermined time period in order to purge the boiler of stale air. Inasmuch as the pneumatic conveyor motor 76 is coupled through power line 135 with the boiler blower 86, it also is actuated concurrently with the blower 86. After the boiler has been purged, the starting pilot 96 is automatically actuated and the presence of the pilot flame is sensed by the scanner 108. The scanner sends a signal to the master control 106 in response to the presence of the flame, permitting the fuel feed process to begin. Accordingly the master control 106 actuates valve 104 so as to feed fuel to the supporting pilot 102, and simultaneously opens dust fuel control valve 136 and supplies power to agitator motor 44 and screw conveyor motors l8 and respectively. This starts the rotation of agitator 38 and screw conveyor 68, the actuation of screw conveyor 16 being dependent upon the level of the dust fuel in the bin as determined by level sensors 24 and 26 in the manner previously described.

Thereafter fuel dust flows through inlet conduit 80 into the combustion chamber 88, such flow being variably modulated by controller 56 responsive to boiler pressure sensing device 62, while the supply of combustion air is concurrently regulated so as to provide proper fuel-air ratio and energy input responsive to boiler demands.

If, during the operation of the boiler, the scanner 108 should indicate the absence of a flame in the combustion chamber, it transmits a signal to the master control 106 which promptly closes dust fuel control valve 136 and supporting pilot valve 104, and also interrupts power to the respective agitator and screw conveyor motors so as to stop the introduction of fuel into the combustion chamber. The previously described starting cycle is then re-initiated.

If the level of fuel dust in the bin 22 should fall below a predetermined limit, as sensed by a minimum level sensor 138 of the same construction as level sensors 24 and 26, a signal is transmitted through line 140 to the master conrol 106 causing interruption of the dust fuel feed to the boiler in the same manner as though the combustion flame were interrupted. In such case the boiler may either be shut down or, if desired, the circuits of the master control 106 can be arranged in a conventional fashion to automatically place the boiler exclusively on an alternate fuel supply, such as natural gas or oil. The purpose of interrupting the dust fuel sup ply prior to the complete emptying of the bin 22 is to insure that, when the problem of resupplying the bin with fuel is eventually corrected, there will be an imme diate fuel supply still available in the bin to permit the normal operation of the boiler starting cycle.

The use of dust-type fuels other than sanderdust, for example coal dust, in a system embodying the foregoing fuel metering and combustion principles is within the scope of the present invention. Moreover, although steam generation is the preferred application of the system, other combustion-type energy generators such as air heaters are also contemplated, with energy demands possibly being indicated by alternative parameters such as temperature. The terms and expressions which have been employed in the foregoing abstract and specification are used therein as terms of description and not of limitation, and there is no intention, in the use of such terms and expressions, of excluding equivalents of the features shown and described or portions thereof, it being recognized that the scope of the invention is defined and limited only by the claims which follow.

What is claimed is:

l. A boiler adapted for utilizing primarily dust-type fuel in its combustion chamber, said boiler having a source of dust fuel, an elongate liquid-jacketed combustion chamber extending substantially the length of said boiler surrounded throughout its length by a liquid, a dust fuel inlet conduit connected at one end to said source of dust fuel and having discharge port means at the other end located within said liquid-jacketed combustion chamber for introducing dust fuel from said source directly into the interior of said liquid-jacketed combustion chamber prior to the ignition of. any of said dust fuel so that combustion of said dust fuel is initiated within said liquid-jacketed combustion chamber, fuel metering apparatus for introducing said dust-type fuel into said combustion chamber through said inlet conduit at a predetermined mass flow rate, and controller means for automatically varying said predetermined mass flow rate in response to variations in the vapor pressure of said boiler.

2. The boiler of claim 1, said boiler being of the multi-pass firetube-type further comprising liquid-jacketed elongate gas tube means, communicating with one end of said combustion chamber, extending substantially the length of said boiler and being surrounded throughout its length by a liquid for receiving combustion products from the interior of said combustion chamber.

3. A boiler adaptable for utilizing primarily dust-type fuel in its combustion chamber, wherein the improvement comprises a boiler diffuser having at least one dust fuel inlet conduit and a supporting pilot mounted adjacent the face of said diffuser for introducing said dust fuel and a fuel other than said dust fuel respectively into the combustion air pattern emitted from the face of said diffuser, said supporting pilot including control means for introducing said other fuel continuously with the introduction of said dust fuel so as to continuously support the combustion of said dust fuel.

4. A multi-pass firetube boiler adaptable for utilizing primarily dust-type fuel in its combustion chamber, said boiler having a burner assembly located at one end thereof, wherein the improvement comprises trap means coupled with the interior of said combustion chamber for retaining within said chamber gross particles which may be present in said dust-type fuel to insure complete combustion thereof, said trap means comprising a boiler extension section adaptable to be inserted between the door and body of said boiler on the end thereof opposite said burner, said extension section having a trap adjacent its bottom portion and interior baffle means for preserving the original combustion gas flow pattern through said firetube boiler.

5. The boiler of claim 1 wherein said fuel metering apparatus comprises a metering bin located in advance of said fuel inlet conduit for receiving dust-type fuel of variable density from said source of dust fuel, agitating means within said bin for homogenizing said dust fuel in said bin thereby equalizing the density thereof, and metering means for discharging said homogenized dust fuel from said bin at a predetermined mass flow rate preparatory to said fuels introduction into said liquidjacketed combustion chamber, said metering means including means for preventing; any compaction of said dust fuel during said metering thereof to a density greater than that of said homogenized fuel in said bin so as to insure against any uncontrolled variation in said predetermined mass flow rate of said fuel.

6. The boiler of claim 1 including a supporting pilot mounted within said liquid-jacketed combustion chamber for introducing a fuel other than said dust fuel into said combustion chamber, said supporting pilot including control means for introducing said other fuel continuously with the introduction of said dust fuel so as to continuously support the combustion of said dust fuel.

7. A method for burning dust-type fuel in a boiler of the type having an elongate combustion chamber extending substantially the length thereof and a liquidholding chamber surrounding said combustion chamber throughout its length, said method comprising:

a. introducing combustion air into said combustion chamber;

b. introducing dust fuel into said combustion chamber prior to the ignition of any of said dust fuel;

of introducing a fuel other than said dust fuel into said combustion chamber continuously with the introduction of said dust fuel, thereby continuously supporting the combustion of said dust fuel.

9. The boiler of claim 3 wherein said diffuser face has directional aperture means formed therein for emitting combustion air into the combustion chamber of said boiler in a swirling pattern, and directional discharge means attached to said dust fuel inlet conduit for directing dust-type fuel substantially tangentially into said swirling pattern of said diffuser.

' UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT NO. 3,902,436

0 DATED 1 September 2, 1975 lN\/ ENTOR(S) Leslie C. Turner and Harry Cockreham It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Col. 3, Llne 64 Change "pln" to bin--.

Col. 7, Line 61 Change "mamner" to -manner-.

g Signed and Scaled this ninth Day of Marc h1976 [SEAL] Arrest.

RUTH c. MASON c. MARSHALL DANN A Arr s ing Officer Commissioner ufParems and Trademarks 

1. A boiler adapted for utilizing primarily dust-type fuel in its combustion chamber, said boiler having a source of dust fuel, an elongate liquid-jacketed combustion chamber extending substantially the length of said boiler surrounded throughout its length by a liquid, a dust fuel inlet conduit connected at one end to said source of dust fuel and having discharge port means at the other end located within said liquid-jacketed combustion chamber for introducing dust fuel from said source directly into the interior of said liquid-jacketed combustion chamber prior to the ignition of any of said dust fuel so that combustion of said dust fuel is initiated within said liquid-jacketed combustion chamber, fuel metering apparatus for introducing said dust-type fuel into said combustion chamber through said inlet conduit at a predetermined mass flow rate, and controller means for automatically varying said predetermined mass flow rate in response to variations in the vapor pressure of said boiler.
 2. The boiler of claim 1, said boiler being of the multi-pass firetube-type further comprising liquid-jacketed elongate gas tube means, communicating with one end of said combustion chamber, extending substantially the length of said boiler and being surrounded throughout its length by a liquid for receiving combustion products from the interior of said combustion chamber.
 3. A boiler adaptable for utilizing primarily dust-type fuel in its combustion chamber, wherein the improvement comprises a boiler diffuser having at least one dust fuel inlet conduit and a supporting pilot mounted adjacent the face of said diffuser for introducing said dust fuel and a fuel other than said dust fuel respectively into the combustion air pattern emitted from the face of said diffuser, said supporting pilot including control means for introducing said other fuel continuously with the introduction of said dust fuel so as to continuously support the combustion of said dust fuel.
 4. A multi-pass firetube boiler adaptable for utilizing primarily dust-type fuel in its combustion chamber, said boiler having a burner assembly located at one end thereof, wherein the improvement comprises trap means coupled with the interior of said combustion chamber for retaining within said chamber gross particles which may be present in said dust-type fuel to insure complete combustion thereof, said trap means comprising a boiler extension section adaptable to be inserted between the door and body of said boiler on the end thereof opposite said burner, said extension section having a trap adjacent its bottom portion and interior baffle means for preserving the original combustion gas flow pattern through said firetube boiler.
 5. The boiler of claim 1 wherein said fuel metering apparatus comprises a metering bin located in advance of said fuel inlet conduit for receiving dust-type fuel of variable density from said source of dust fuel, agitating means within said bin for homogenizing said dust fuel in said bin thereby equalizing the density thereof, and metering means for discharging said homogenized dust fuel from said bin at a predetermined mass flow rate preparatory to said fuel''s introduction into said liquid-jacketed combustion chamber, said metering means including means for preventing any compaction of said dust fuel during said metering thereof to a density greater than that of said homogenized fuel in said bin so as to insure against any uncontrolled variation in said predetermined mass flow rate of said fuel.
 6. The boiler of claim 1 including a supporting pilot mounted within said liquid-jacketed combustion chamber for introducing a fuel other than said dust fuel into said combustion chamber, said supporting pilot including control means for introducing said other fuel continuously with the introduction of said dust fuel so as to continuously support the combustion of said dust fuel.
 7. A method for burning dust-type fuel in a boiler of the type having an elongate combustion chamber extending substantially the length thereof and a liquid-holding chamber surrounding said combustion chamber throughout its length, said method comprising: a. introducing combustion air into said combustion chamber; b. introducing dust fuel into said combustion chamber prior to the ignition of any of said dust fuel; c. mixing said dust fuel with said combustion air and dispersing a mixture of said air and said dust fuel throughout the interior of said combustion chamber; d. surrounding said combustion chamber throughout its length with a liquid; e. thereafter igniting said mixture and burning said mixture within said liquid-surrounded combustion chamber; and f. removing the products of combustion from said combustion chamber.
 8. The method of claim 7 including the further step of introducing a fuel other than said dust fuel into said combustion chamber continuously with the introduction of said dust fuel, thereby continuously supporting the combustion of said dust fuel.
 9. The boiler of claim 3 wherein said diffuser face has directional aperture means formed therein for emitting combustion air into the combustion chamber of said boiler in a swirling pattern, and directional discharge means attached to said dust fuel inlet conduit for directing dust-type fuel substantially tangentially into said swirling pattern of said diffuser. 